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Organisationseinheit der BAM
Glass-ceramics are noted for their unusual combination of properties and manifold commercialized products for consumer and specialized markets. Evolution of novel glass and ceramic processing routes, a plethora of new compositions, and unique exotic nano- and microstructures over the past 60 years led us to review the Definition of glass-ceramics. Well-established and emerging processing methods, such as co-firing, additive manufacturing, and laser patterning are analyzed concerning the core requirements of processing glass-ceramics and the Performance of the final products. In this communication, we propose a revised, updated definition of glass-ceramics, which reads “Glass-ceramics are inorganic, non-metallic materials prepared by controlled crystallization of glasses via different processing methods. They contain at least one type of functional crystalline phase and a residual glass. The volume fraction crystallized may vary from ppm to almost 100%”.
Aim: To observe the variation in accumulation of Fusarium and Alternaria mycotoxins across a topographically heterogeneous field and tested biotic (fungal and bacterial abundance) and abiotic (microclimate) parameters as explanatory variables.
Methods and Results: We selected a wheat field characterized by a diversified topography, to be responsible for variations in productivity and in canopy-driven microclimate. Fusarium and Alternaria mycotoxins where quantified in wheat ears at three sampling dates between flowering and harvest at 40 points.
Tenuazonic acid (TeA), alternariol (AOH), alternariol monomethyl ether (AME), tentoxin (TEN), deoxynivalenol (DON), zearalenone (ZEN) and deoxynivalenol-3-Glucoside (DON.3G) were quantified. In canopy temperature, air and soil humidity were recorded for each point with data-loggers. Fusarium spp. as trichothecene producers, Alternaria spp. and fungal abundances were assessed using qPCR. Pseudomonas fluorescens bacteria were quantified with a culture based method. We only found DON, DON.3G, TeA and TEN to be ubiquitous across the whole field, while AME, AOH and ZEN were only occasionally detected. Fusarium was more abundant in spots with high soil humidity, while Alternaria in warmer and drier spots. Mycotoxins correlated differently to the observed explanatory variables: positive correlations between DON accumulation, tri 5 gene and Fusarium abundance were clearly detected.
The correlations among the others observed variables, such as microclimatic conditions, varied among the sampling dates. The results of statistical model identification do not exclude that species coexistence could influence mycotoxin production.
Conclusions: Fusarium and Alternaria mycotoxins accumulation varies heavily across the field and the sampling dates, providing the realism of landscapescale studies. Mycotoxin concentrations appear to be partially explained by biotic and abiotic variables.
Significance and Impact of the Study: We provide a useful experimental design and useful data for understanding the dynamics of mycotoxin biosynthesis in wheat.
Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in, the amount of thermal SiO2 oxide on (100) and (111) orientation Si wafer substrates in the thickness range 1.5 - 8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing-incidence x-ray reflectrometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterised by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.
The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The remaining data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonadeous contamination equivalent to ~1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-Ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and, critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2) deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, then these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.
The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 µm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.
Crystallization behavior in different atmospheres (air, Ar, and 7% H2/Ar) of lithium iron phosphate glass (33Li2O33Fe2O31Nb2O5–33P2O5 (LFNP)) powders with different sizes of 2–1000 µm was examined. The crystallization peak temperature (Tp) in Ar and 7% H2/Ar decreased with decreasing the particle size of glass powders, but the value of Tp in air was independent of particle size. The crystallized glass obtained by heating to Tp showed the formation of the α-Li3Fe2(PO4)3 and LiFePO4 crystalline phases. Fe2O3 crystals were formed only in the inside of crystallized glass plates in the heating in air. The crystallization of LiFePO4 was largely enhanced in the particle size of <2 µm during the heating in Ar and 7% H2/Ar atmospheres. The main crystallization mechanism in LFNP glass was found to be surface crystallization. Significant shrinkages were observed for glass compacts (pellets) in the heating in 7% H2/Ar. These results suggest that controlling particle sizes and atmospheres enables the design the morphology of LiFePO4 crystals in LFNP glass.
The high-resolution synchrotron-based imaging stations at the BAMline (BESSY) and TopoTomo (ANKA)
(2008)
The BAMline at the BESSY light source in Berlin and the TopoTomo beamline at the ANKA synchrotron facility in Karlsruhe (both Germany) operate in the hard X-ray regime (above 6 keV) with similiar photon flux density. For typical imaging applications, a double multilayer monochromator or a filtered white beam is used. In order to optimise the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 16-bit dynamic range slow-scan CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. The moderate flux of both beamlines compared to other 3rd generation light sources is compensated by a dedicated scintillator concept. For selected applications, X-ray beam collimation has proven to be a reliable approach to increase the available photon flux density. Absorption contrast, phase contrast, holotomography and refraction-enhanced imaging are used depending on the application. Additionally, at the TopoTomo beamline digital white beam synchrotron topography is performed, using the digital X-ray pixel detectors installed.
The aim of the joint project ViPQuali (Virtual Product Qualification) was to describe a components ageing behaviour in a given environment, by numerical simulation.
Having chosen polypropylene (PP) as the material, which does not show sensitivity to moisture, the relevant weathering parameters of the doseresponse functions could be limited to spectral irradiance and temperature.
In artificial irradiation tests, for PP plates of varied stabiliser content, spectral sensitivity as well as temperature dependence of irradiation-caused crack formation was quantified. For that purpose, samples were exposed both to artificial weathering tests at various constant temperatures and to spectrally resolved irradiation. The temperature dependence could be modelled by an Arrhenius fit. For fitting the spectral sensitivity, a plateau function was chosen. Subsequently, the stabiliser content was parameterised and extrapolated.
The formed dose–response functions were incorporated into a Computational Fluid Dynamics (CFD) software program, simulating the environment of a sample within a Phoenix-exposed IP/DP (Instrument Panel/Door Panel box) box, based on sun position and weather conditions, including radiation interactions. Observed local effects as well as the general ageing advance of PP hats are compared with respect to simulation and experiment.
Resulting from this project, for this most simple example of PP of varied stabiliser content, the time to failure can be estimated for each weathering exposure environment with known time-resolved irradiance and temperature conditions.
The crystallization behavior of sodium ion conductive Na2MnP2O7 glass was examined to clarify the crystallization mechanism. The formation of thermodynamically metastable phase, layered Na2MnP2O7, at the surface of the glass occurred. Heat treatment at 430 °C for 3 h lead to surface crystals of Na2MnP2O7 oriented with the (101) direction perpendicular to the sample surface. As the heat treatment temperature increased, the glass-ceramic samples deformed, and the presence numerous micro bubbles due to dissolved water was detected.
Ceramics and their composites are in general brittle materials because they are predominantly made up of ionic and covalent bonds that avoid dislocation motion at room temperature. However, a remarkable ductile behavior has been observed on newly developed 11 mol.% ceria-stabilized zirconia (11Ce-TZP) composite containing fine alumina (8 vol.% Al2O3) and elongated strontium hexa-aluminate (8 vol.% SrAl12O19) grains. The as-synthesized composite also has shown full resistance to Low Temperature Degradation (LTD), relatively high strength and exceptionally high Weibull modulus, allowing its use in a broader range of biomedical applications. In this study, to deepen the understanding of plastic deformation in Ce-TZP based composites that could soon be used for manufacturing dental implants, different mechanical tests were applied on the material, followed by complete microstructural characterization. Distinct from pure Ce-TZP material or other zirconia-based ceramics developed in the past, the material here studied can be permanently strained without affecting the Young modulus, indicating that the ductile response of tested samples cannot be associated to damage occurrence. This ductility is related to the stress-induced tetragonal to monoclinic (t-m) zirconia phase transformation, analogue to Transformation-Induced Plasticity (TRIP) steels, where retained austenite is transformed to martensite. The aim of this study is to corroborate if the observed plasticity can be associated exclusively to the zirconia t-m phase transformation, or also to microcraking induced by the transformation. The t-m transformed-zones produced after bending and biaxial tests were examined by X-ray refraction and SEM/TEM coupled with Raman. The results revealed that the observed elastic-plastic behavior occurs without extensive microcracking, confirming a purely elastic-plastic behavior driven by the phase transformation (absence of damage).
Glasses with compositions of 21Gd2O3-63MoO3-(16-x)B2O3-xTeO2 (mol%) (x= 0, 2, 4, 8) were prepared using a conventional melt quenching technique, and the crystallization behavior of ferroelastic β′-Gd2 MoO4)3 Crystals was examined to clarify the mechanism of self-powdering phenomenon and to design bulk crystallized glasses. It was found that the self-powdering phenomenon appeared significantly during the crystallization at temperatures near the crystallization peak temperature, but the phenomenon is suppressed in the crystallization at temperatures much higher than the glass transition temperature. It was also found that the substitution of TeO2 for B2O3 in the base glasses suppresses the self-powdering phenomenon and consequently bulk crystallized glasses were obtained in the glass with x=8 mol%. The densities at room temperature of the base glasses are d =4.755–4.906 g/cm3, being much higher than the value of d=4.555 g/cm3 for β′-Gd2(MoO4)3 crystal. It is proposed that the stresses in the inside of crystals induced by large density differences (i.e., large molar volume differences) between the glassy phase and crystals might be relaxed effectively in the glasses containing TeO2 with weak TeeO bonds and fragile character.
Mobility particle size spectrometers (MPSS) belong to the essential instruments in aerosol science that determine the particle number size distribution (PNSD)in the submicrometer size range. Following calibration procedures and target uncertainties against standards and reference instruments are suggested for a complete MPSS quality assurance program: a) calibration of the CPC counting efficiency curve (within 5% for the plateau counting efficiency; within 1 nm for the 50% detection efficiency diameter), b) sizing calibration of the MPSS, using a certified polystyrene latex (PSL) particle size standard at 203 nm (within 3%), c) intercomparison of the PNSD of the MPSS (within 10% and 20% of the dN/dlogDP concentration for the particle size range 20 – 200 nm and 200 to 800 nm, respectively), and d) intercomparison of the integral PNC of the MPSS (within 10%). Furthermore, following measurement uncertainties have been investigated: a) PSL particle size standards in the range from 100-500nm match within 1% after sizing calibration at 203 nm. b) Bipolar diffusion chargers based on the radioactive nuclides Kr85, Am241 and Ni63 and a new ionizer based on corona discharge follow the recommended bipolar charge distribution, while soft X-ray-based charges may alter faster than expected. c) The use of a positive high voltage supply show a 10% better performance than a negative one. d) The intercomparison of the integral PNC of an MPSS against the total number concentration is still within the target uncertainty at an ambient pressure of approximately 500 hPa.
3-Aminovinylquinoxalines are readily accessible from (hetero)aryl glyoxylic acids or heterocyclic π-nucleophiles by consecutive four- and fivecomponent syntheses in the sense of an activation-alkynylation-cyclocondensation-addition sequence or glyoxylation-alkynylation-cyclocondensation-addition sequence in good yields. The title compounds are highly fluorescent with pronounced emission solvatochromicity and protochromic fluorescence quenching. Time-resolved fluorescence spectroscopy furnishes radiative and nonradiative fluorescence decay rates in various solvent polarities. The electronic structure is corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic effects.
Die Berechnung von Wärmebrücken unter stationären und instationären Randbedingungen, die Optimierung von Wärmespeichern, die Beurteilung sowohl wärmeschutz- als auch brandschutztechnischer Maßnahmen und Energiebedarfsrechnungen setzen die Kenntnis thermischer Eigenschaften, u.a. der Wärmeleitfähigkeit Lambda und der spezifischen Wärmekapazität c, in Abhängigkeit der Temperatur voraus. Im Rahmen einer Zusammenarbeit der EMPA-Dübendorf und der BAM-Berlin wurde ein Kurzzeit-Prüfverfahren mit anschließender numerischer Auswertung entwickelt, das eine simultane Bestimmung dieser beiden Größen ermöglicht. In dem Band wird über das Kurzzeit-Prüfverfahren, das numerische Auswerteverfahren und die Resultate der Messungen an einigen ausgewählten Baustoffen berichtet.
The therapy of eye tumors with fast protons is an excellent tool giving very high local control rates. At the Helmholtz-Zentrum Berlin (HZB) almost 1800 patients were treated since 1998. A 2 MV Tandetron was installed as injector for the k = 132 HZB cyclotron. Using the standard 358 duoplasmatron ion source with direct extraction of negative hydrogen ions an extremely stable proton beam can be delivered, both on the short-term and the long-term scale. The hair-needle filaments made from thoriated tungsten wires have safe operation times of more than 1000 h.
The material properties of recycled concrete aggregates (RCA) are
correlated to the sorting accuracy of the former demolition waste. Impurities like
wood, clay bricks or gypsum can lead to inferior building material properties. Harmful
substances like heavy metals or organic pollutants should be minimised as well.
Hence the non-concrete materials have to be separated from the concrete material
stream. This can be done during the demolition process by using selective
dismantling techniques. Alternatively a variety sorting and classifying techniques to
purify the crushed concrete can be utilized.
A research project, funded by the Federal Ministry for the Environment, Nature
Conservation and Nuclear Safety, investigated the possibilities of gaining recycled
concrete aggregates of a high quality for the reuse in the production of concrete. The
work focuses especially on how gypsum respectively sulphates in the crushed
concrete can be reduced. Sulphates can impair the setting behaviour of concrete
and also damage set concrete by causing expansion. Therefore the content of
sulphates in RCA is restricted by guidelines and standards in Germany.
Generally, gypsum in construction waste originates from interior fittings like gypsum
walls, floor screeds, plaster boards and also plaster. Most of these materials can be
reconstructed using selective dismantling techniques. This can be achieved either by
manual labour or by using mechanical equipment e.g. to remove floor screeds by
milling. Depending on the specific deconstruction site it can be more effective and/or
more environmentally compatible to remove sulphates by treating the crushed
concrete. Applicable treatments for sulphate reduction include dry processes like
manual sorting of gypsum wall blocks as well as wet treatments e.g. jigging.
In addition this research project an environmental performance evaluation was
undertaken to assess different techniques for reducing sulphates in recycled
concrete aggregates.
Zur Untersuchung der Initiierungsvorgänge und dem Wachstumsverhalten lokaler Korrosionskeime auf nichtrostenden Stählen wurde eine neue elektrochemisch-mikroskopische Messmethode entwickelt. Bei dieser Messmethode wird durch Einsatz eines Echtfarben- Konfokalmikroskops mit Immersionsobjektiv das empfindliche elektrochemische Rauschmessverfahren um eine bildgebende Messkomponente erweitert. Ziel dieser Untersuchung war es, diskrete Rauschmesssignale visuell detektierbaren Korrosionserscheinungen auf der Stahloberfläche nahezu in Echtzeit zuzuordnen. Auf Grund der notwendigen Anforderungen an einen in situ Messaufbau wurde im Rahmen dieser Untersuchung ein neuartiges selbstklebendes Folienelektrodensystem, bestehend aus Gegen- und Bezugselektrode, entwickelt, das für die in situ Messung zum Einsatz kam. Die in situ Untersuchungen wurden an dem austenitischen Chrom-Nickel-Stahl 1.4301 durchgeführt. Als Ergebnis der Experimente konnten Stromtransienten im nA- bis μA-Bereich messtechnisch erfasst werden und mikroskopisch kleinen Korrosionskeimen, die sowohl stabil wie auch metastabil auf der Stahloberfläche auftraten, diskret und zeitnah zugeordnet werden. Weiterhin konnten mit Hilfe der Konfokaltechnik die Volumina und die Mantelflächen der einzelnen Lochdefekte ermittelt werden, sodass durch Auswertung und Kombination der elektrochemischen und mikroskopischen Messergebnisse erstmalig die Korrosionsstromdichte bestimmt werden konnte, die bei der Initiierung der lokalen Lochkeime aufgetreten ist. Damit konnte die Funktionalität und die hohe Empfindlichkeit des elektrochemisch-mikroskopischen Messverfahrens im Rahmen dieser Untersuchung erfolgreich verifiziert werden.